The viewing of multimedia on personal computers, such as personal computers running a version of the Microsoft Windows operating system, has become very common-place. Such multimedia content is frequently derived from television-type video sources. That is, a videotape from a television program or similar content may be viewed in real-time on a computer.
Processing television images for display by a computer is a complex and intensive task, however, because of the nature of television images themselves as compared to the nature of images typically displayed by computers. A television image is usually an interlaced video image. This means that each image consists of two separate fields, one field including the odd scan lines of the image, and the other field including the even scan lines of the image. Displaying each field in rapid order creates the illusion of one image. In this manner, even though the transmission of video information may be limited to a given number of scan lines, the resolution of the video information actually displayed is doubled.
This is illustrated by reference to FIG. 1. Field 100 includes lines 102. Each of lines 102 corresponds to an odd line of an image. Field 104 includes lines 106, each of which corresponds to an even line of an image. Thus, displaying fields 100 and 104 in rapid succession in an appropriate manner results in interlaced image 108, where lines 102 are the odd lines of the image, and lines 106 are the even lines of the image. Interlaced video is known in the art, and is used in such application as television programming, etc.
Computers, however, usually do not use interlaced video, but rather progressive video. Rather than displaying two fields of scan lines--one field for even lines, and one field for odd lines--in rapid succession to create the illusion of a single image, progressive video displays only one field of scan lines--including both even and odd scan lines--which is the image itself. Technically, this is a less complex manner by which to display images. However, it is generally incompatible with source video that is interlaced. Progressive video is also known in the art.
There are a number of solutions within the prior art to convert interlaced video to progressive video, so that it can be displayed by a computer. A technically simple solution, but undesirable from a display standpoint, is to merely use only one of the two fields present in the interlaced source video as the only field of the progressive output video. Thus, only the odd or even scan lines of the interlaced source video are shown in the progressive output video actually displayed. This results in a jagged look to the display of the progressive video, and may result in blank scan lines where the non-displayed even or odd lines carried vertical detail information. However, this solution is technically easy to accomplish, because minimal processing is taking place: both fields of the interlaced video are input, but only one field is actually displayed.
A more sophisticated approach to convert interlaced video to progressive video is to perform line doubling on one of the fields of the interlaced video, and then combine the resulting image with a line doubled version of the other field of the interlaced video. This "de-interlaced" image can then be displayed in a progressive manner at the frame rate instead of at the field rate. However, this solution requires that the second field be precisely positioned over the first field when it is being combined with the first field. The lines of the second field that were derived in the doubling process must be aligned with the source lines of the first field. The lines of the first field that were derived in the doubling process must be aligned with the source lines of the second field. If precise positioning is not accomplished, a jitter or shaking effect will be seen in fine detail areas on the resulting displayed progressive video. This line doubling and combination solution is also less than desirable because it requires significant processing to achieve. For example, the typical personal computer does not have sufficient processing power to perform line doubling and combination.
Therefore, there is a need for a manner by which to generate progressive output video from interlaced source video that results in a high-quality image when the output video is displayed by a computer. Such a solution should not require processing that cannot be accomplished by the typical personal computer. Thus, the solution should provide high-quality images in accordance with a relatively straightforward algorithm.